Fuel Injection System The purpose of the fuel injection system is to precisely inject a metered amount of fuel at the correct time. Based on the input sensor signals, the ECMs programming will decide when to turn each injector on and off. Fuel Delivery System The purpose of the fuel delivery system is to quietly deliver the proper volume of fuel at the correct pressure. The fuel delivery system must also meet emission and safety regulations. Major components are: • Fuel Pump. • Fuel Pump ECU. • Pressure Regulator. • Fuel Pressure Control Circuit. • Fuel Lines. • Fuel Tank. • Fuel Filter. • Pulsation Damper. • Fuel Injectors. • Inertia Switch. FUEL SYSTEMS #1 - OVERVIEW Page 1 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Return Fuel Delivery System When the fuel pump is activated by the ECM, pressurized fuel flows out of the tan, through the fuel filter to the fuel rail and up to the pressure regulator. The pressure regulator maintains fuel pressure in the rail at a specified value. Fuel in excess of that consumed by engine operation is returned to the tank by a fuel return line. A pulsation damper, mounted on the fuel rail, is used on many engines to dampen pressure variations in the fuel rail. The injectors, when turned on by the ECM deliver fuel into the intake manifold. When the fuel pump is turned off by the ECM, a check valve in the fuel pump closes maintaining a residual pressure in the fuel system. Returnless Fuel Delivery System When the fuel pump is activated by the ECM pressurized fuel flows from the pump to the pressure regulator. At the pressure regulator excess fuel is directed to the bottom of the fuel tank and pressurized fuel is sent out of the fuel tank, through the fuel filter, pulsation damper, and into the fuel rail. When the ECM turns on the injectors fuel is delivered into the intake manifold. Fuel pressure in this system is maintained at a constant and higher pressure, 44-50 psi (301- 347 kPa) than the return fuel system. ECM programming and a higher fuel pressure eliminates the need for a vacuum modulated pressure regulator. FUEL SYSTEMS #1 - OVERVIEW Page 2 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. The returnless fuel delivery system was adopted because it lowers evaporative emissions since no heated fuel is returned to the fuel tank. On the return fuel delivery system, fuel heated by the engine returns to the fuel tank and has warmer fuel creating more fuel vapors. Fuel Pump The fuel pump is mounted in the tank and immersed in fuel. The fuel cools and lubricates the pump. When current flows through the motor, the armature and impeller rotate. The impeller draws fuel in through a filter and discharges pressurized fuel through the outlet port. The fuel pump's pumping capacity is designed to exceed engine requirements. This insures that there will always be enough fuel to meet engine demands. An outlet check valve, located in the discharge outlet, maintains a residual fuel pressure in the fuel system when the engine is off. This improves starting characteristics and reduces vapor- lock. Without residual fuel pressure, the system would have to be pressurized each time the engine was started and this would increase engine starting (cranking) time. When a hot engine is shut off, fuel temperature in the lines around the engine increases. Keeping the system pressurized increases the boiling point of the fuel and prevents the fuel from vaporizing. A pressure relief valve will open if the fuel system becomes restricted. This is a safety device to prevent the fuel lines from rupturing and damage to the pump. FUEL SYSTEMS #1 - OVERVIEW Page 3 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. On many models the fuel pump is part of the fuel pump assembly. This assembly contains the filters, pressure (fuel system only), sending unit, and fuel pump. Many of the components can be serviced separately. FUEL SYSTEMS #1 - OVERVIEW Page 4 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Jet Pump The jet pump is an additional pump used when the fuel tank bottom is divided into two chambers. Excess fuel flowing through the fuel return passes through a venturi. This creates a low pressure area around the venturi, and this action will draw the fuel out of Chamber B, and sends it into Chamber A. FUEL SYSTEMS #1 - OVERVIEW Page 5 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Fuel Pump Controls A variety of fuel pump control circuits and controls have been used over the years. The following basic methods are: • ON/OFF Control by ECM. • ON/OFF Control by Fuel Pump Switch. • ON/OFF Two Speed Control with a Resistor. • ON/OFF Two Speed Control with Fuel Pump ECU. • ON/OFF Three Speed Control with Fuel Pump ECU. The most accurate way of determining the type of fuel control circuit is to look up the circuit in the appropriate EVVD. FUEL SYSTEMS #1 - OVERVIEW Page 6 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. The following describes the basic methods of fuel pump control. An essential point to remember is that the fuel pump operates only when the engine is cranking or running. ON/OFF Control by ECM The following is an explanation of how the fuel pump circuit is activated. Engine Start When the engine is cranking, current flows from the IG terminal of the ignition switch to the L1 coil of the EFI main relay, turning the relay on. At the same time, current flows from the ST terminal of the ignition switch to the L3 coil of the circuit opening relay, turning it on to operate the fuel pump. The fuel pump is now supplying fuel to the fuel injection system. Note: The circuit opening relay in this example is ground side switched. Engine Running Once the engine starts and the ignition key is moved to the ON (IG) position, current to the L3 coil is shut off, but the ECM will keep the fuel pump on through coil L2 as long as the ECM receives an NE signal. If the NE signal is lost at any time after starting, the ECM turns the fuel pump off. FUEL SYSTEMS #1 - OVERVIEW Page 7 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Engine Stopped When the engine stops, the NE signal to the ECM stops. This turns off the transistor, thereby cutting off the flow of current to the L2 coil of the circuit opening relay. As a result, the circuit opening relay opens turning off the fuel pump. Note: The resistor R and the capacitor C in the circuit-opening relay are for the purpose of preventing the relay contacts from opening when current stops flowing in coil L2 due to electrical noise (fuel pumps controlled by the ECM) or to sudden drops in the intake air volume (fuel pumps controlled by fuel pump switch). They also serve to prevent sparks from being generated at the relay contacts. On some models, an L3 coil is not provided in the circuit- opening relay. ON/OFF Control by Fuel Pump Switch The fuel pump switch is found on older vehicles using a Vane Air Flow Meter. The air moves the vane when the engine is running closing the fuel pump switch. The following is an explanation of circuit operation. Engine Start When the engine is cranking, current flows from the IG terminal of the ignition switch to the L1 coil of the EFI main relay, turning the relay on. Current also flows from the ST terminal of the ignition switch to the L3 coil of the circuit-opening relay, turning it on to operate the fuel pump. After the engine starts, the cylinders begin drawing in air, causing the measuring plate inside the air flow meter to open. This turns on the fuel pump switch, which is connected to the measuring plate, and current flows to the L2 coil of the circuit-opening relay. FUEL SYSTEMS #1 - OVERVIEW Page 8 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Engine Running After the engine starts and the ignition switch is turned from ST back to IG, current flowing to the L3 coil of the circuit-opening relay is cut off. However, current continues to flow to the L2 coil while the engine is running due to the fuel pump switch inside the air flow meter being on. As a result, the circuit-opening relay stays on, allowing the fuel pump to continue operating. Engine Stopped When the engine stops, the measuring plate completely closes and the fuel pump switch is turned off. This cuts off the flow of current to the L2 coil of the circuit-opening relay. As a result, the circuit-opening relay goes off and the fuel pump stops operating. Two Speed Fuel Pump Control Large displacement engines require a higher volume of fuel during starting and heavy load conditions than small displacement engines. High capacity fuel pumps are used to meet the demand, but they produce more noise and consume more power. To overcome these disadvantages and increase pump life, a two speed fuel pump control is used. ON/OFF Two Speed Control with a Resistor This type uses a double contact relay and a series limiting resistor. FUEL SYSTEMS #1 - OVERVIEW Page 9 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. FUEL SYSTEMS #1 - OVERVIEW Page 10 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. [...].. .FUEL SYSTEMS #1 - OVERVIEW ON/OFF Two Speed Control with Fuel Pump ECU This type is similar to other systems, but uses a Fuel Pump ECU In this system, however, ONOFF control and speed control of the fuel pump is performed entirely by the Fuel Pump ECU based on signals from the ECM In addition, the Fuel Pump ECU is equipped with a fuel pump system diagnosis function When... regulator located above the fuel pump in the fuel tank This type of regulator maintains a constant fuel pressure regardless of intake manifold pressure Fuel pressure is determined by the spring inside the regulator Fuel from the fuel pump overcomes spring pressure and some fuel is bypassed into the fuel tank Fuel pressure is non-adjustable High Temperature (Pressure Up) Fuel Pressure Control Some engines... servicing the fuel lines Connectors can be the threaded type or the quick connector style Page 17 © Toyota Motor Sales, U.S.A., Inc All Rights Reserved FUEL SYSTEMS #1 - OVERVIEW Fuel Tank The fuel tank is designed to safely contain the fuel and evaporative emissions Typically, it houses the fuel pump assembly and rollover protection valves Fuel Filters Typically, there are two fuel filters in the fuel delivery... volts) to the FPC terminal of the Fuel Pump ECU The Fuel Pump ECU then supplies full battery power to the fuel pump Low Speed After the engine starts, during idle and light loads, the ECM outputs a low signal (about 2.5 volts) to the Fuel Pump ECU Then, the Fuel Pump ECU supplies less voltage (about 9 volts) to the fuel pump Three Speed Fuel Pump Control With this system, the fuel pump is controlled in 3... signal to the fuel pump ECU The fuel pump ECU then applies battery power to the fuel pump causing the fuel pump to operate at high speed Medium Speed Under heavy loads at low speed, the ECM sends a 2.5 volt signal to the fuel pump control The fuel pump ECU applies about 10 volts to the fuel pump This is considered medium speed Page 11 © Toyota Motor Sales, U.S.A., Inc All Rights Reserved FUEL SYSTEMS #1... ECM sends a 1.3 volt signal to the fuel pump ECU The fuel pump ECU applies 8.5 volts to the fuel pump, preventing excessive noise and decreasing power consumption Inertia Switch The fuel pump inertia switch shuts off the fuel pump when the vehicle is involved in a collision, minimizing fuel leakage Page 12 © Toyota Motor Sales, U.S.A., Inc All Rights Reserved FUEL SYSTEMS #1 - OVERVIEW Operation The... keep the fuel pressure at a constant value, 226-265 kPa (38-44 psi) As air pressure changes, such as climbing from low to high altitude, fuel rail pressure decreases because there is less force on the diaphragm Page 15 © Toyota Motor Sales, U.S.A., Inc All Rights Reserved FUEL SYSTEMS #1 - OVERVIEW Constant Pressure Regulator Returnless Fuel Delivery System) The Returnless Fuel Delivery System uses... delivery system The first filter is the fuel pump filter located on the suction side of the fuel pump This filter prevents debris from damaging the fuel pump The second filter, located between the pump and fuel rail, removes dirt and contaminates from the fuel before it is delivered to the injectors This filter removes extremely small particles from the fuel, the injectors require extremely clean fuel. .. clean fuel The filter may be located in the fuel tank as part of the fuel pump assembly or outside the tank in the fuel line leading to the fuel rail The filter is designed to be maintenance-free with no required service replacement Page 18 © Toyota Motor Sales, U.S.A., Inc All Rights Reserved FUEL SYSTEMS #1 - OVERVIEW A restricted fuel filter will prevent fuel from reaching the injectors Therefore,... pressure This allows more fuel to return to the fuel tank decreasing pressure in the fuel rail Opening the throttle increases manifold pressure With less vacuum on the diaphragm spring pressure will increase restricting fuel flow to the fuel tank This increases pressure in the fuel rail Atmospheric Modulated Pressure Regulator The atmospheric modulated pressure regulator modifies fuel pressure with changes . Fuel Injection System The purpose of the fuel injection system is to precisely inject a metered amount of fuel at the correct time. Based on the input. injector on and off. Fuel Delivery System The purpose of the fuel delivery system is to quietly deliver the proper volume of fuel at the correct pressure. The fuel delivery system must also meet. components are: • Fuel Pump. • Fuel Pump ECU. • Pressure Regulator. • Fuel Pressure Control Circuit. • Fuel Lines. • Fuel Tank. • Fuel Filter. • Pulsation Damper. • Fuel Injectors. •